High Molecular Weight Polymers Research Articles

Humic acid as an efficient and reusable catalyst for one pot three-component green synthesis of 5-substituted 1H-tetrazoles in water.

Humic acid is a non toxic, inexpensive, easily available high-molecular weight polymer. A simple and facile one pot three-component synthesis of 5-substituted 1H-tetrazoles from aldehydes, hydroxyamine hydrochloride and sodium azide using humic acid as an efficient catalyst in water is described. The method reported has several advantages such as high to excellent yields, easy work-up, mild reaction conditions, use of water as a green solvent, and a commercially available, nontoxic and reusable catalyst.

Spray drying of pectin obtained from Citrus Sinensis waste

Polysaccharides are high molecular weight polymers that have functional groups, which can be used as sites to derivate or bind specific ligands. Pectin is a polysaccharide that is obtained from plant resources mainly from citrus plants. It is a widely used product in the food and in the pharmaceutical industry for its thickener, stabilizing and gelling properties. The objective of this work was to establish a pectin drying process obtained by acid hydrolysis from citrus waste by spray dry. An acid extraction process with the dry and ground plant material was used. The influence of the inlet and outlet temperatures on the yield and drying speed was evaluated by an experimental design 32 replicated at the central point. With the best variant, five batches were developed at laboratory scale and one batch at bank scale, evaluating the obtained material by infrared spectroscopy and scanning electron microscopy. The results of experimental design showed that the temperature does not influence significantly the yield, but it does affect the speed of the drying. An input-output temperature ratio of 200/80 ºC was established as the best drying variant. The batches prepared on a laboratory scale showed a yield higher than 85.0% and a drying speed higher than 0.7 L / h. The yield of the batch on a bank scale was 90%. The degree of esterification was 63.5%, indicative of a high degree of methoxylation pectins. The results show that the drying process is adequate to obtain pharmaceutical grade pectin.

Aromatic polycarbonates bearing pendant maleimide groups via functional monomer approach: synthesis and characterization

A new bisphenol containing pendant maleimide group, viz., 4, 4’-(5-maleimidopentane-2, 2-diyl) diphenol (BPA-MA), was synthesized starting from commercially available 4, 4’-bis (4-hydroxyphenyl) pentanoic acid. Aromatic (co)polycarbonates possessing pendant maleimide groups were synthesized by solution polycondensation of BPA-MA or varying mixtures of BPA-MA and bisphenol-A (BPA) with triphosgene in dry dichloromethane in the presence of triethylamine as a base. Inherent viscosities and number average molecular weights of (co)polycarbonates were in the range 0.46–0.66 dL/g and 24,600-36,700, respectively, indicating the formation of reasonably high molecular weight polymers. Tough, transparent, and flexible films could be cast from chloroform solutions of these (co)polycarbonates. (Co)polycarbonates were characterized using FT-IR, 1H NMR, 13C NMR spectroscopy, XRD, TGA and DSC analysis. The chemical modification of a representative copolycarbonate containing pendant maleimide groups was carried out quantitatively using thiol-maleimide Michael addition reaction with two thiol compounds, namely, 4-chlorothiophenol and 1-adamantanethiol. Additionally, it was demonstrated that copolycarbonate containing pendant maleimide groups could be used to form insoluble cross-linked gel by reaction with a multifunctional thiol cross-linker, namely, pentaerythritol tetrakis(3-mercaptopropionate).

Fast Ring‐Opening Polymerization of 1,2‐Disubstituted Epoxides Initiated by a CoIII‐Salen Complex

AbstractPolyethers are an important class of polymers that find numerous applications. Ring‐opening polymerization of various 1,2‐disubstituted epoxides initiating a commercial, and well‐defined CoIII‐Salen complex is investigated in this paper. Remarkable reactivity (0.01% CoIII loadings, TOF up to 19200 h−1) is discovered in this transformation. High molecular weight polymers (up to 80 kg mol−1) are produced. In particular, polyether from ring‐opening polymerization of 1,4‐dihydronaphthalene oxide exhibits a glass transition temperatures (Tg) of up to 108 °C. By investigating the relationship between polymerization reactivity and counter ion in the CoIII complex, as well as the properties of the resultant polyethers, a cationic mechanism through an oxonium species is proposed.

Synthesis and characterization of aminophenolate-ligated rare-earth metal amide complexes and their catalytic activity for lactides polymerization

Amine elimination of Ln[N(SiMe3)2]3(μ-Cl)Li(THF)3 with aminophenol H[ON] {H[ON] = 2-(CH2NC5H10)-4,6-tBu2-C6H3OH} in 1:2 molar ratio in THF gave the monometallic rare-earth metal amide complexes [ON]2LnN(SiMe3)2 (Ln = Yb (1), Y (2), Gd (3), Sm (4), Nd (5)) in 57%—73% isolated yields. All these complexes were characterized by elemental analysis. The molecular structures of complexes 1–4 were determined by single crystal X-ray diffraction. These complexes are highly active for l-lactide polymerization to give high molecular weight polymers with unimodal molecular weight distributions. In addition, these complexes can also initiate rac-lactide polymerization with high activity to afford heterotactic-rich polylactides.

Modular Assembly of Host-Guest Metal-Phenolic Networks Using Macrocyclic Building Blocks.

The manipulation of interfacial properties has broad implications for the development of high-performance coatings. Metal-phenolic networks (MPNs) are an emerging class of responsive, adherent materials. Herein, host-guest chemistry is integrated with MPNs to modulate their surface chemistry and interfacial properties. Macrocyclic cyclodextrins (host) are conjugated to catechol or galloyl groups and subsequently used as components for the assembly of functional MPNs. The assembled cyclodextrin-based MPNs are highly permeable (even to high molecular weight polymers: 250-500 kDa), yet they specifically and noncovalently interact with various functional guests (including small molecules, polymers, and carbon nanomaterials), allowing for modular and reversible control over interfacial properties. Specifically, by using either hydrophobic or hydrophilic guest molecules, the wettability of the MPNs can be readily tuned between superrepellency (>150°) and superwetting (ca. 0°).

Modular Assembly of Host–Guest Metal–Phenolic Networks Using Macrocyclic Building Blocks

AbstractThe manipulation of interfacial properties has broad implications for the development of high‐performance coatings. Metal–phenolic networks (MPNs) are an emerging class of responsive, adherent materials. Herein, host–guest chemistry is integrated with MPNs to modulate their surface chemistry and interfacial properties. Macrocyclic cyclodextrins (host) are conjugated to catechol or galloyl groups and subsequently used as components for the assembly of functional MPNs. The assembled cyclodextrin‐based MPNs are highly permeable (even to high molecular weight polymers: 250–500 kDa), yet they specifically and noncovalently interact with various functional guests (including small molecules, polymers, and carbon nanomaterials), allowing for modular and reversible control over interfacial properties. Specifically, by using either hydrophobic or hydrophilic guest molecules, the wettability of the MPNs can be readily tuned between superrepellency (>150°) and superwetting (ca. 0°).

Liquid Metal Nanoparticles as Initiators for Radical Polymerization of Vinyl Monomers.

Sonication of gallium or gallium-based liquid metals in an aqueous solution of vinyl monomers leads to rapid free radical polymerization (FRP), without the need for conventional molecular initiators. Under ambient conditions, a passivating native oxide separates these metals from solution and renders the metal effectively inert. However, sonication generates liquid metal nanoparticles (LMNPs) of ∼100 nm diameter and thereby increases the surface area of the metal. The exposed metal initiates polymerization, which proceeds via a FRP mechanism and yields high molecular weight polymers that can form physical gels. Spin trapping EPR reveals the generation of free radicals. Time-of-flight secondary ion mass spectrometry measurements confirm direct polymer bonding to gallium, verifying the formation of surface-anchored polymer grafts. The grafted polymers can modify the interfacial properties, that is, the preference of the metal particles to disperse in aqueous versus organic phases. The polymer can also be degrafted and isolated from the particles using strong acid or base. The concept of physically disrupting passivated metal surfaces offers new routes for surface-initiated polymerization and has implications for surface modification, reduction reactions, and fabrication of mechanically responsive materials.

Comparative assessment of drag reduction efficiencies of polymer solutions and surfactants at low temperatures

The antiturbulent efficiency of solutions of high molecular weight polymers and that of micellar systems of surfactants are compared. The effect of the structural organization of polymer solutions and colloidal systems on their antiturbulent efficiency is shown. Hydrodynamic and physicochemical approaches are used to interpret the experimental results. It is shown that the use of polymers as drag reducing agents in main oil pipelines is more preferable at low liquid temperatures in northern latitudes (the Arctic).

Consequences of superfine grinding treatment on structure, physicochemical and rheological properties of transglutaminase-crosslinked whey protein isolate

Impacts of superfine grinding treatment (0, 2, 4, 6, 8 or 10 h) on structure, physicochemical and rheological properties of transglutaminase (TGase)-crosslinked whey protein isolate (WPI) were investigated. Size exclusion chromatography showed that high molecular weight polymers were formed in TGase-treated sWPI (WPI treated with superfine grinding), whereas its consumption of free amino groups reached the maximum at grinding 8 h and 10 h. With the milling time extended from 0 to 10 h, particle size of the TGase-crosslinked sWPI gradually increased. Emission spectrum shifted from 338.6 nm to 340.6 nm after sWPI treated with TGase. Meanwhile, TGase-crosslinked sWPI had higher apparent viscosity, emulsifying properties than TGase-crosslinked WPI, but the solubility of TGase-crosslinked sWPI was lower than sWPI. Superfine grinding treatment remarkably increased β-sheet and random compositions in TGase-crosslinked sWPI. These findings indicated that superfine grinding treatment could enhance the TGase cross-linking degree, and improve rheological properties in TGase-crosslinked WPI.

Modeling of spunbond formation process of polymer nonwovens

Spunbond process used in nonwoven manufacturing employs the system which combines fiber-forming and bonding together. A high molecular weight polymer, e.g., PP (polypropylene), can be used as a raw material resulting in fibers of 15–35 μm in diameter formed by the spunbond process. The present work aims at simulations of the spunbond process before the bonding stage with a goal of predicting the resulting nonwoven laydown and its three-dimensional architecture, and potentially in future, the corresponding laydown properties. The quasi-one-dimensional equations of fiber dynamics are used as a key element of the multi-fiber modeling. The air flow field is comprised of a section with one-dimensional flow used for stretching and a subsequent section with three-dimensional axisymmetric flow used for fiber deposition. The fiber motion in air flux shaped by the surrounding attenuator is simulated accounting for polymer melt quenching and solidification. The laydown properties, such as the 3-D structure of the web, mass distribution, elevation distribution and fabric cross-sectional structure, are also predicted using post-processing of the numerical results.

Slickwater hydraulic fracture propagation: near-tip and radial geometry solutions

We quantify the importance of turbulent flow on the propagation of hydraulic fractures (HF) accounting for the addition of friction reducing agents to the fracturing fluid (slickwater fluid). The addition in small quantities of a high molecular weight polymer to water is sufficient to drastically reduce friction of turbulent flow. The maximum drag reduction (MDR) asymptote is always reached during industrial-like injections. The energy required for pumping is thus drastically reduced, allowing for high volume high rate hydraulic fracturing operations at a reasonable cost. We investigate the propagation of a hydraulic fracture propagating in an elastic impermeable homogeneous solid under a constant (and possibly very high) injection rate accounting for laminar and turbulent flow conditions with or without the addition of friction reducers. We solve the near-tip HF problem and estimate the extent of the laminar boundary layer near the fracture tip as a function of a tip Reynolds number for slickwater. We obtain different propagation scalings and transition time scales. This allows us to easily quantify the growth of a radial HF from the early-time turbulent regime(s) to the late-time laminar regimes. Depending on the material and injection parameters, some propagation regimes may actually be bypassed. We derive both accurate and approximate solutions for the growth of radial HF in the different limiting flow regimes (turbulent smooth, rough, MDR) for the zero fracture toughness limit (corresponding to the early stage of propagation of a radial HF). We also investigate numerically the transition(s) between the early-time MDR regime to the late-time laminar regimes (viscosity and toughness) for slickwater fluid. Our results indicate that the effect of turbulent flow on high rate slickwater HF propagation is limited and matters only at early times (at most during the first minutes for industrial hydraulic fracturing operations).

Rheological Considerations for Binder Development in Direct Ink Writing of Energetic Materials

AbstractAdditive manufacturing is a promising approach to prepare highly specifically defined materials with unique dimensions, gradients in material attributes and on‐demand properties. For energetic materials applications, it is particularly exciting for its potential to create lattice and cellular structures and gradient solids to focus or dissipate energy. However, there are significant challenges to overcome, particularly in obtaining the very high particle content (>80 vol % particles), while still being manufacturable. This work focuses on the polymer binder used in an energetic materials system and aims to understand how its characteristics affect the viscosity and printability of the suspension. Two different types of polymer binders are examined: (a) high molecular weight polymer in a solvent and (b) polymerizable smaller molecules that were cured via UV light. We show that the suspension viscosity is primarily controlled by the particle volume fraction for the UV curable binder, while both the particle volume fraction and polymer molecular weight influence the response in the case of the polymer/solvent binder. Both binder types can be tuned to provide printable suspensions that result in lines of consistent width and 3D disc‐shaped objects, indicating that both paths are good potential directions for future formulations for polymer bonded explosives prepared via additive manufacturing.

THE PAYNE EFFECT: PRIMARILY POLYMER-RELATED OR FILLER-RELATED PHENOMENON?

ABSTRACT The hysteretic softening at small dynamic strains (Payne effect)—related to the rolling resistance and viscoelastic losses of tires—was studied as a function of particle size, filler volume fraction, and temperature for carbon black (CB) reinforced uncrosslinked styrene–butadiene rubber (SBR) and a paste-like material composed of CB-filled paraffin oil. The low-strain limit for dynamic storage modulus was found to be remarkably similar for CB-filled oil and the CB-filled SBR. Small-angle X-ray scattering (SAXS) measurements on the simple composites and detailed data analysis confirmed that the aggregate structures and nature of filler branching/networking of carbon black were virtually identical within oil compared to the high molecular weight polymer matrix. The combined dynamic rheology and SAXS results provide clear evidence that the deformation-induced breaking (unjamming) of the filler network—characterized by filler–filler contacts that are percolated throughout the material—is the main cause for the Payne effect. However, the polymer matrix does play a secondary role as demonstrated by a reduction in Payne effect magnitude with increasing temperature for the CB-reinforced rubber, which was not observed to a significant extent for the oil–CB system.

Brush-Like Polymers and Entanglements: From Linear Chains to Filaments.

Dynamics of melts and solutions of high molecular weight polymers and biopolymers is controlled by topological constraints (entanglements) imposing a sliding chain motion along an effective confining tube. For linear chains, the tube size is determined by universal packing number Pe, the number of polymer strands within a confining tube that is required for chains to entangle. Here we show that in melts of brush-like (graft) polymers, consisting of linear chain backbones with grafted side chains, Pe is not a universal number and depends on the molecular architecture. In particular, we use coarse-grained molecular dynamics simulations to demonstrate that the packing number is a nonmonotonic function of the ratio Rnsc/Rng of the size of the side chains Rnsc to that of the backbone spacer between neighboring grafting points Rng. This parameter characterizes the degree of mutual interpenetration between side chains of the same macromolecule. We show that Pe of brush-like polymers first decreases with increasing side chain grafting density in the dilute side chain regime (Rnsc < Rng), then begins to increase in the regime of overlapping side chains (Rnsc > Rng), approaching the value for linear chains in the limit of densely grafted side chains. This dependence of the packing number reflects a crossover from chain-like entanglements in systems with loosely grafted side chains (comb-like polymers) to entanglements between flexible filaments (bottlebrush-like polymers). Our simulation results are in agreement with the experimental data for the dependence of a plateau modulus on the molecular architecture of graft poly(n-butyl acrylates) and poly(norbornene)-graft-poly(lactide) melts.

A comparison of the physico‐mechanical properties of two proprietary PLA based resorbable graft materials

Background A wide range of auto-, allo- and xenograft materials are used in reconstructive implant related therapy. Such materials used as barrier membranes confer a number of properties related to their manufacturing and processing. Resorbable synthetic polymers+ PLA, PGA's and Caprolactone are widely used polymers in medical devices and an understanding of the physico- mechanical properties including TGA, DSC, TMA, and PGC will assist in the selection of optimal properties. Aim/Hypothesis The aims of this study were to compare the physico-mechanical behaviour of two polymer based resorbable graft materials+ Guidor and Polyoss to better understand how their properties can be correlated to their clinical behaviour. Materials and Methods Samples of two proprietary PLA based membrane materials were selected for study; Guidor (Sunstar Chemicals; Germany) and Polyoss R (Ossform pty; Australia). The material samples were subjected to DSC, TGA, TMA and GPC to gain an understanding of their properties. Ossform is synthesised as a filament for 3D printing so samples of raw material, filament and printed material, pre and post-gamma irradiation were investigated to study the effects of any of material processing. Gel Permeation Chromatography (GPC)was performed using an Agilent Technologies 1260 with (THF). The peaks were detected using a refractive index detector (40 ⁰C). Thermo-Gravimetric Analysis (TGA)was performed using a TA SDT650. A 3 to 7 mg polymer sample was used for measurements. The sample was heated to 600 C at 10 ⁰C/min under a flow of nitrogen (50 ml/min). The Td was calculated at 5% weight loss. Differential Scanning Calorimetry (DSC) was performed using a TA DSC250. Tg, Tc, Tm, and ∆Hm were identified. Results Guidor is a PLA based material manufactured as a barrier membrane for periodontal and implant reconstruction. TGA demonstrated a second peak in the plot at 30°C for Guidor as compared with Polyoss. This indicated approximately 15% of citric acid esters in the sample. Guidor had a low molecular weight of 54-56000 and an Mn of 88-90000. The degradation temperature was also low at 227-231°C. There was little difference in properties between the first and second TGA scan. Polyoss-R is a medical grade PLA based polymer designed for the production of grafts, membranes and shells by 3D printing. Four samples were analysed granular (PG), filament (PF), gamma sterilised filament (PFG) and printed sample (PS). Polyoss – R is a higher molecular weight polymer with a mwt of 159-285000 and Mn 111-196000. It had a PD of 1.4-1.5 and a midpoint degradation temperature of 262–316°C. The difference in the DSC for PG in the first and second run can be attributable to a reorganisation of the polymer. Conclusion and Clinical Implications Synthetic polymers offer significant benefits in the development of stable and three-dimensional grafts and barrier membranes. Guidor is a well established material and its measured properties correlate well its clinical performance. Its low molecular weight will give it a fairly short resorption time (6–8 weeks). Whilst that for Polyoss-R will be longer (c.12 weeks). This investigation the production processes can produce successful bioresorbable polymers suitable for clinical use.

Crosslinked Quaternized Poly(arylene ether benzonitrile) Membranes for Vanadium Redox Flow Batteries

Development of membrane separators is important to decrease cross-over and enhance efficiency and durability of non-aqueous redox flow batteries. Desired properties of the membranes for the application include (a) selective ion permeability, (b) high conductivity and (c) good chemical and mechanical stability in operating conditions of redox flow batteries. Our approach to satisfy these criteria is synthesizing cation-functionalized nitrile-containing polyaromatics, poly(arylene ether benzonitrile)s, for membrane separators. While these membranes exhibited good performances in an aqueous vanadium redox flow battery (VRFB) system, in non-aqueous systems where acetonitrile is used as electrolytes, the membranes could not be utilized due to their limited mechanical strength. To endure the harsh operating condition of non-aqueous VRFB, we developed crosslinked quaternized poly(arylene ether benzonitrile)s. A series of high molecular weight polymers with tertiary amine groups were synthesized via aromatic nucleophilic substitution polycondensation followed by the simultaneous quaternization and crosslinking reactions. In this presentation we will discuss the membrane properties and the electrochemical performance of these membranes in terms of cycling efficiencies, vanadium permeation and membrane durability. The applicability of crosslinked quaternized poly(arylene ether benzonitrile) membranes in non-aqueous VRFB systems will be summarized. Acknowledgement This work is fully supported by Laboratory Directed Research & Development, Los Alamos National Laboratory. The submission of the manuscript is approved by LANL (LA-UR-19-23557)

Factors affecting fractal patterns obtained by electroless deposition in polymer

Electroless deposition of silver has been studied experimentally in a polymer (chitosan) with different molecular weight (∼50 000–190 000 Da and ∼600 000 Da). Transport of ions in polymers involves various dynamical processes having different time scales. The time scale of ion dynamics depends on the number of monomer chains in the polymer, i.e., the molecular weight of the polymer. Polymers of high molecular weight contain regular arrangement of long chains of monomers which generally leads to high crystallinity. Copper, zinc and aluminum wires have been used for different reaction rates in the polymer-Ag salt solution. Anisotropy of the polymer-salt solution varies due to the change in the ion dynamics in high molecular weight polymer as compared to the low molecular weight polymer. Varying anisotropy leads to different aggregation patterns around the reactive metal wires. X-ray diffraction has been performed to determine the crystallinity while the voltage-time measurement has been done to validate the aggregation process. Effect of air exposure/oxidation on the growth patterns has also been considered as the adsorption of oxygen ions changes with the change in the crystallinity of the polymer.

Low temperature effect on ATRP of styrene and substituted styrenes enabled by SaBOX ligand

A series of side-armed bisoxazoline (SaBOX) ligands have been designed and prepared, which exhibited high activity under (SARA) ATRP conditions even at low temperatures. Notably, both polymerization rate and controllability on molecular weight (MW) were significantly improved by using 4-MeOSt as monomer instead of styrene under the conditions in this work, which is significantly different from the previous reports that only oligomers were produced in the conventional ATRP of 4-MeOSt due to the presence of cationic species. Systematic studies indicated that SaBOX ligand enabled the low polymerization temperature, which is necessary to suppress the cationic polymerization process and produce high MW polymers rather than oligomers during the ATRP of 4-MeOSt. Meanwhile, the highly active SaBOX ligand guaranteed the high polymerization rate and good controllability. Moreover, by employing these SaBOX ligands, the controlled ATRP of styrene and substituted styrenes could be successfully achieved at low temperatures (−30 °C–25 °C), producing polymers with molecular weights close to theoretical values and relatively narrow molecular weight distributions (Đs = 1.2–1.5). More notably, the triad syndiotacticity (rr) of polystyrene was gradually enhanced from 48% to 62% by lowering the polymerization temperature, which demonstrated that the stereospecificity could be tuned in ATRP of styrene for the first time. The improved syndiotacticity and the subdued side reactions indicated the superiority and necessity of the polymerization at low temperature for ATRP in some aspects.

Condensation of all-cis-tetraphenylcyclotetrasiloxanetetraol in ammonia: new method for preparation of ladder-like polyphenylsilsesquioxanes

One-step method for the preparation of polyphenylsilsesqui oxane by condensation of all-cis-1,3,5,7-tetraphenyl-1,3,5,7 tetrahydroxycyclotetrasiloxane in liquid ammonia has been developed. This method makes it possible to produce high molecular weight polymers with regular structure in the absence of organic solvent. The structure of the polymer product was confirmed by 1H and 29Si NMR spectroscopy, GPC, IR spectroscopy, powder X-ray diffraction and viscosimetry.